Opportunistic Screening for Low Bone Mineral Density in Routine Computed Tomography Scans: A Brazilian Validation Study

Introduction/background: Osteoporotic fractures are a major health concern worldwide due to high mortality rates, deterioration in quality of life, and elevated healthcare costs related to hospital treatment. However, most patients who sustain an osteoporotic fracture have never been formally screened for osteoporosis. Opportunistic screening of osteoporosis through conventional computed tomography (CT) scans performed for unrelated reasons could help identify patients with low bone mass. There are currently no studies validating the opportunistic screening of low bone mass through CT in South America. The aim of our study is to assess whether conventional CT scans could be used for the opportunistic screening of osteopenia and osteoporosis in Brazilian patients. Methodology: Patients who underwent unenhanced CT and dual-energy X-ray absorptiometry (DXA) scans within a six-month interval were assessed retrospectively. Mean CT attenuation was measured in the first lumbar vertebra (L1) in axial, coronal, and sagittal planes and compared to their respective DXA T-scores; vertebral fractures were assessed in the sagittal plane. Potential thresholds suggestive of low bone mass density (BMD) were established using receiver operating characteristics analysis. Results: 491 patients were included (93.2 % female; mean age of 64.1 +/- 9.8 years; mean interval of 63.5 days between scans). Mean L1 CT attenuation was significantly lower in osteopenic and osteoporotic patients in all CT planes (p < 0.001). Positive linear correlations were found between DXA T-scores and the average L1 attenuations in all CT planes (p < 0.001). An average L1 attenuation equal or below 100 Hounsfield Units (HU) in the sagittal plane identified low BMD (osteopenia or osteoporosis) with a specificity of 96.3 % and a positive predictive value of 96 %. In contrast, an average L1 attenuation above 180 HU demonstrated a sensitivity of 97.6 % and a negative predictive value of 94.9 % for detecting osteoporosis. Patients with L1 sagittal attenuation at or below 100 HU exhibited a significantly higher prevalence of vertebral fractures (prevalence ratio: 8.67; p < 0.001). An online calculator based on the results of this study is freely available at www. osteotc.com.br. Conclusions: Routine CT scans can identify probable low bone density (osteopenia or osteoporosis) in Brazilian patients without additional costs or radiation exposure. Opportunistic CT screening does not substitute formal bone mineral density assessment; instead, it assists in identifying patients who may benefit from it.